Coal Burning power plants in the United States and around the world produce tens of millions of tons of fly ash annually. The single largest beneficial application for fly ash is as a mineral admixture in concrete product markets. However, only a small percentage of annual fly ash production is utilized in concrete markets.
Emission Control technologies, implemented to reduce toxic air pollutants from coal burning power plants have had the negative consequence of producing fly ash with elevated levels of carbon or carbon that is highly absorptive/reactive. The resulting fly ash is unusable in the concrete industry and therefore must be land filled which increases costs to the electric power industry.
Fly ash utilization in concrete markets solves massive disposal problems and results in significantly improved concrete quality. During the concrete production process, air entraining agents (AEA's) are added to create a microscopic matrix of air bubbles. This air void matrix in concrete provides escape chambers for water that freezes/thaws due to changes in temperature. The freezing and thawing activity of water in concrete is a primary contributor to pre-mature cracking and long term durability issues.
AEA's have a high affinity for carbon which effectively de-activates the AEA's leaving concrete with reduced levels of air voids necessary for long term durability. Accordingly, in order to make use of the large abundance of fly ash produced annually, it is necessary to neutralize the reactive carbon existing in the fly ash.
The currently existing treatment systems and methods do not solve this problem. Fly ash is an extremely fine material that tends to absorb moisture in air resulting in a packing effect when stored or transported at a power plant. Proactive steps must be taken to prevent clumping and bridging as fly ash treatment is administered. Failure to do so results in treatment which is inconsistent and unpredictable. Also, fly ash is produced in massive quantities daily and must be rapidly treated to keep pace with production levels. Due to the extreme material handling aspects and production levels of fly ash, existing methods of chemical treatment merely dose fly ash as it free falls via gravity out of the silos in clumps, resulting in incomplete contact with the chemical agent. Further, inconsistent fly ash loading time makes it impossible to accurately dose chemical agents required for consistent homogeneous contact with carbon. Agents currently used in the treatment of fly ash may not be specific for carbon, may have activity similar to air-entrainment agents (thereby causing AEA dosing problems), have biological activity, may be leached from concrete by water, or may chemically degrade. Further, the carbon particles have a minimal opportunity to interact with the treatment compound. For these reasons—existing methods of treatment simply utilize AEA's to pre-dose the fly ash.
The invention solves the root problem of neutralizing the reactive carbon particles residing within the fly ash allowing the fly ash to be utilized in concrete production. The invention also reduces truck loading times by effectively treating the carbon as it exits the boiler en-route to the fly ash silo. Since trucking, or transportation, of the fly ash is a significant aspect of the cost, there is a need for a system and method of fly ash treatment such as the one described herein. The invention is designed to provide homogeneous application of a sacrificial agent to fly ash in order to provide fly ash having reduced carbon levels which are adequate for use in the concrete industry.